1. Field of the Invention
The present invention relates generally to image projection systems, and in particular, to an image projection system that permits a remote user or viewer to focus at least a portion of a projected image.
2. Description of the Related Art
Display systems for projecting images onto screens and other suitable surfaces for viewing by large audiences are known. Devices used to project images onto screens include document cameras, overhead projectors, slide projectors, and video cameras. The projected images can be generated by computer programs or by light passing through film slides.
A desirable feature of a display system is to enable a member of the audience to enter information interactively into the system to during the presentation. The prior art provides an arrangement whereby a user directs a high-intensity light from a device, such as a light pen or a laser pointer, onto a projected image to provide control information to the system. Such a system is described in U.S. Pat. No. 5,515,079. In this system, a sensor detects a spot of light cast onto a projected image by a hand-held laser pointer. The position of the spot relative to the image is determined. In turn, this position information is used as a control input. By pulsing the laser beam, the light spot can emulate a computer mouse click. In this manner, the laser pointer can be used to control the display. For example, an audience member with a laser pointer can vary the presentation sequence of a slide show.
The prior art also provides projection systems that include a computer for generating images used in conjunction with a liquid crystal display (LCD). The LCD is placed on the stage of an overhead projector. The projector shines light through the LCD to produce the projected image. In addition to projecting the image, the system can also project anything that appears on the computer monitor, including a computer cursor. Consequently, a user sitting at the computer can move the cursor across the image and control the display using a keyboard or mouse.
U.S. Pat. No. 5,115,230 discloses a projection system that is integrated into a teleconferencing system. This arrangement allows a projected image to be displayed at remote locations using computer display terminals or other projection systems.
A limitation of the above-mentioned projection systems is that they typically provide an average focus capability, where the center of the screen is in clear focus, while the outer edges of the projected image are less focused due to the differences in projection distance. Known automatic focusing devices usually produce a single focal point at the center of the image. Generally, to focus on different portions of an image, a user must manually adjust the projector focus. This can be inconvenient when presenting a slide show before a large audience.
It is desirable to have an image display system that allows a user or member of the audience to automatically focus a selected portion of the displayed image without manual intervention. It is also desirable to include a selective auto-focusing capability in a display system that also permits a remote viewer to input control information using either a computer cursor or a light generating device, such as a laser pointer.